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Influence of substrate temperature on morphology and behavior under cyclic thermal load of gas flow sputtered zirconia coatings

: Rösemann, N.; Ortner, K.; Petersen, J.; Stöwer, M.; Bäker, M.; Bräuer, G.; Rösler, J.


Surface and coatings technology 324 (2017), S.7-17
ISSN: 0257-8972
Fraunhofer IST ()
gas flow sputtering; reactive sputtering; yttria stabilized zirconia; thermal barrier coatings; substrate temperature; morphology; microstructure; grain orientation; thermal cycling; failure mechanism

The aim of this work is to gain an understanding of the influence of substrate temperature during deposition on the resulting microstructure and crystallographic properties of gas flow sputtered (GFS) partially yttria stabilized zirconia coatings (PSZ). PSZ coatings were deposited on a FeCrAl-Alloy substrate, varying the substrate temperature between 500 °C and 800 °C. Regardless of the substrate temperature, all coatings were columnar, but varied in their morphology. Four different groups of sub-microstructures, each defined by a substrate temperature range, were identified based on morphology and X-ray diffraction (XRD) pattern. The two low-temperature groups exhibit a novel microstructure characterized by three dense ridges at intervals of 120° converging at the column center. Supported by these ridges small stacked plates lead to a featherlike porosity. The XRD pattern revealed a monoclinic fraction, besides the tetragonal and/or cubic one, and a 〈111〉 growth direction. Higher temperatures diminish the monoclinic fraction until it vanishes at 800 °C accompanied by a change in growth direction to 〈100〉.Thermal cycling experiments were conducted between 1050 °C and 100 °C. Macroscopic spallation occurred for one group while the other samples were intact after the end of the experiment at 1300 cycles. Microscopic delaminations were found between a pure alumina scale and a mixed oxide zone, consisting of zirconia particles embedded into an alumina matrix. A hypothesis was proposed explaining the observed failure mode.